My iMac bluetooth sometimes disconnect all bluetooth devices and often not stable

In full. My iMac bluetooth connection seems to be a little bit annoying because it's more like the bluetooth connection is unstable which sometimes causing all bluetooth devices disconnected for a few seconds then it will reconnect them all in a few seconds later.

Most of the time it comes with no sign. All bluetooth devices just stop working and see popup says all devices disconnected and then connected. It doesn't laggy mouse cursor and such.

It's been awhile now and I am just thinking, might be I am connecting so many devices such as trackpad, magic keyboard and magic mouse. So I take keyboard out and replace as USB, problem still here.

Finally I am noticing this problem must be done after I am using Bose QC35 because the connection is totally unstable. It's very hard to listen the whole music or watch a movie without an interruption. I did tested with my Macbook Pro, iPad, iPhone etc none of them having this problem.

So the bluetooth is unstable for a long long time but magic devices can keep up with my iMac but bluetooth headphone can't...